Support a two-stage build for separate libimas-core / imas-core packaging (#62)

Author: SimonPinches

CMakeLists.txt

@@ -35,6 +35,13 @@ endif()
 # ##############################################################################
 option(AL_PYTHON_BINDINGS "Build Python bindings" OFF)
 
+# When ON, the al C++ library is not built here; instead it is located with
+# find_package(al-core CONFIG). Enables a two-stage build where libimas-core
+# (the C/C++ library) and imas-core (the Python wrapper) are packaged
+# separately, e.g. as two conda packages.
+option(AL_USE_INSTALLED_CORE
+       "Link Python bindings against a pre-installed al-core (find_package)" OFF)
+
 
 # Configuration options for shared libraries
 # ##############################################################################
@@ -127,8 +134,31 @@ if(WIN32)
   find_package(dlfcn-win32 CONFIG REQUIRED)
 endif()
 
-# build AL_CORE library only if backend is enabled
-if(AL_BACKEND_HDF5 OR AL_BACKEND_MDSPLUS OR AL_BACKEND_UDA OR AL_BACKEND_UDAFAT OR AL_PYTHON_BINDINGS)
+# Two-stage build entry: locate a pre-installed al-core instead of building it.
+# Exposes target `al-core::al` and an unqualified alias `al` so the python/
+# subdirectory and any consumers can link to `al` transparently.
+if(AL_USE_INSTALLED_CORE)
+  find_package(al-core CONFIG)
+  if(NOT al-core_FOUND)
+    message(FATAL_ERROR
+      "AL_USE_INSTALLED_CORE=ON requires an installed al-core that ships "
+      "al-coreConfig.cmake (introduced in IMAS-Core 5.7.1 or later). "
+      "find_package(al-core CONFIG) could not locate it.\n"
+      "Point CMAKE_PREFIX_PATH (or al-core_DIR) at an install prefix that "
+      "contains lib/cmake/al-core/al-coreConfig.cmake — typically the "
+      "stage-1 install tree of this branch. Releases built before this "
+      "change (e.g. IMAS-Core/5.6.0) only ship al-core.pc and will NOT "
+      "satisfy AL_USE_INSTALLED_CORE; either install stage 1 from source "
+      "or wait for a release that includes the CMake package config.")
+  endif()
+  if(NOT TARGET al)
+    add_library(al ALIAS al-core::al)
+  endif()
+endif()
+
+# build AL_CORE library only if backend is enabled and we are not reusing an
+# already-installed al-core
+if((AL_BACKEND_HDF5 OR AL_BACKEND_MDSPLUS OR AL_BACKEND_UDA OR AL_BACKEND_UDAFAT OR AL_PYTHON_BINDINGS) AND NOT AL_USE_INSTALLED_CORE)
 
 # Core dependencies
 set(Boost_USE_MULTITHREADED FALSE)
@@ -199,14 +229,43 @@ add_dependencies( imas_print_version al )
 # ##############################################################################
 
 # Install al library
+include(GNUInstallDirs)
 install(
   TARGETS al
+  EXPORT al-coreTargets
   RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
   LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
   ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
   COMPONENT core
 )
 
+# Export CMake package config so downstream projects (notably the Python
+# wrapper built with AL_USE_INSTALLED_CORE=ON) can `find_package(al-core CONFIG)`.
+include(CMakePackageConfigHelpers)
+set(_al_core_cmake_dir ${CMAKE_INSTALL_LIBDIR}/cmake/al-core)
+install(
+  EXPORT al-coreTargets
+  FILE al-coreTargets.cmake
+  NAMESPACE al-core::
+  DESTINATION ${_al_core_cmake_dir}
+)
+configure_package_config_file(
+  ${CMAKE_CURRENT_SOURCE_DIR}/cmake/al-coreConfig.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/al-coreConfig.cmake
+  INSTALL_DESTINATION ${_al_core_cmake_dir}
+)
+write_basic_package_version_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/al-coreConfigVersion.cmake
+  VERSION ${PROJECT_VERSION}
+  COMPATIBILITY SameMajorVersion
+)
+install(
+  FILES
+    ${CMAKE_CURRENT_BINARY_DIR}/al-coreConfig.cmake
+    ${CMAKE_CURRENT_BINARY_DIR}/al-coreConfigVersion.cmake
+  DESTINATION ${_al_core_cmake_dir}
+)
+
 # TODO: put public heades in a separate directory?
 install(
   FILES ${PUBLIC_HEADER_FILES}
@@ -240,14 +299,15 @@ install(DIRECTORY common TYPE DATA)
 # Install Dummy
 install(TARGETS imas_print_version DESTINATION bin)
 
-# Scikit-build-core entry point for python bindings
+endif() # AL core library: (AL_BACKEND_* OR AL_PYTHON_BINDINGS) AND NOT AL_USE_INSTALLED_CORE
+
+# Scikit-build-core entry point for python bindings — works whether `al` was
+# just built here or imported via find_package(al-core).
 # ##############################################################################
 if(AL_PYTHON_BINDINGS)
   include(skbuild.cmake)
 endif()
 
-endif() # AL core library (AL_BACKEND_HDF5 OR AL_BACKEND_MDSPLUS OR AL_BACKEND_UDA OR AL_BACKEND_UDAFAT OR AL_PYTHON_BINDINGS)
-
 
 # MDSplus models
 # ##############################################################################

cmake/al-coreConfig.cmake.in

@@ -0,0 +1,8 @@
+@PACKAGE_INIT@
+
+include(CMakeFindDependencyMacro)
+find_dependency(Boost COMPONENTS filesystem)
+
+include("${CMAKE_CURRENT_LIST_DIR}/al-coreTargets.cmake")
+
+check_required_components(al-core)

pyproject.toml

@@ -83,6 +83,7 @@ AL_BACKEND_UDA = { env = "AL_BACKEND_UDA", default = "ON" }
 AL_BACKEND_MDSPLUS = { env = "AL_BACKEND_MDSPLUS", default = "OFF" }
 AL_BUILD_MDSPLUS_MODELS = { env = "AL_BUILD_MDSPLUS_MODELS", default = "OFF" }
 AL_PYTHON_BINDINGS = "ON"
+AL_USE_INSTALLED_CORE = { env = "AL_USE_INSTALLED_CORE", default = "OFF" }
 DOWNLOAD_DEPENDENCIES = { env = "DOWNLOAD_DEPENDENCIES", default = "ON" }
 DD_GIT_REPOSITORY = { env = "DD_GIT_REPOSITORY", default = "EMPTY" }
 DD_VERSION = { env = "DD_VERSION", default = "EMPTY" }

python/CMakeLists.txt

@@ -8,6 +8,14 @@ python_add_library(al_defs MODULE ${al_defs_source} WITH_SOABI)
 target_link_libraries(_al_lowlevel PRIVATE Python::NumPy al)
 target_link_libraries(al_defs PRIVATE Python::NumPy al)
 
+if(AL_USE_INSTALLED_CORE)
+  # libal is provided externally (e.g. the libimas-core conda package).
+  # Install only the Python extensions — the dynamic linker resolves libal
+  # at load time via the host's normal library search path / rpath.
+  install(TARGETS _al_lowlevel al_defs DESTINATION imas_core)
+  return()
+endif()
+
 # Handling RPATH in macOS:
 if(APPLE)
   set_target_properties(al PROPERTIES INSTALL_RPATH "@loader_path")

skbuild.cmake

@@ -34,19 +34,36 @@ elseif(NOT ${AL_PYTHON_BINDINGS} MATCHES "[Oo][Nn]")
   message(FATAL_ERROR "AL_PYTHON_BINDINGS=${AL_PYTHON_BINDINGS} not e|editable|no-build-isolation|[Oo][Nn]")
 endif()
 
-add_custom_command(
-  TARGET al POST_BUILD
-    COMMAND 
-      ${CMAKE_COMMAND} -E env 
+if(AL_USE_INSTALLED_CORE)
+  # `al` is an ALIAS to an imported target — it is not built in this tree,
+  # so it cannot carry a POST_BUILD hook. Drive pip wheel from the custom
+  # target itself, and put it in ALL so `cmake --build` triggers it.
+  add_custom_target(al-python-bindings ALL
+    COMMAND
+      ${CMAKE_COMMAND} -E env
       CMAKE_ARGS=${CMAKE_ARGS}
-      SKBUILD_BUILD_DIR=${CMAKE_CURRENT_BINARY_DIR}/{wheel_tag} 
+      SKBUILD_BUILD_DIR=${CMAKE_CURRENT_BINARY_DIR}/{wheel_tag}
       ${Python_EXECUTABLE}
-        -m pip wheel 
+        -m pip wheel
         ${CMAKE_CURRENT_SOURCE_DIR}
-	${PIP_OPTIONS}
-	--wheel-dir ${CMAKE_CURRENT_BINARY_DIR}/dist/
-)
-add_custom_target(al-python-bindings DEPENDS al)
+        ${PIP_OPTIONS}
+        --wheel-dir ${CMAKE_CURRENT_BINARY_DIR}/dist/
+  )
+else()
+  add_custom_command(
+    TARGET al POST_BUILD
+      COMMAND
+        ${CMAKE_COMMAND} -E env
+        CMAKE_ARGS=${CMAKE_ARGS}
+        SKBUILD_BUILD_DIR=${CMAKE_CURRENT_BINARY_DIR}/{wheel_tag}
+        ${Python_EXECUTABLE}
+          -m pip wheel
+          ${CMAKE_CURRENT_SOURCE_DIR}
+          ${PIP_OPTIONS}
+          --wheel-dir ${CMAKE_CURRENT_BINARY_DIR}/dist/
+  )
+  add_custom_target(al-python-bindings DEPENDS al)
+endif()
 set_target_properties(
   al-python-bindings PROPERTIES DIST_FOLDER ${CMAKE_CURRENT_BINARY_DIR}/dist/)
 install(CODE "execute_process(COMMAND ${Python_EXECUTABLE}